Just how often Kim Jong-un has used the train to travel inside North Korea is not known.

But his father, who famously hated flying and had a penchant for a playboy lifestyle, is said to have decked the train out for lavish parties, bouts of heavy drinking and karaoke on his many journeys by rail.

According to an account published in 2002 by Konstantin Pulikovsky, a Russian official who accompanied Kim Jong-il on a three-week trip to Moscow in 2001, the train carried cases of bordeaux and beaujolais from Paris. Passengers could also feast on live lobster and barbecued pork.

Kim Jong-il's first trip abroad on the train as leader came in 2000, six years after his father's death. It has now been six years since Kim Jong-il's death.

The most important feature of the heavily armoured train might be security.

According to South Korean reports, North Korea has 90 special train carriages in total and operates three trains in tandem when a leader is travelling — an advance train to check the rails, the train with the leader and his immediate entourage, and a third train behind for everyone else.

Advanced communications and flat screen TVs have been installed so the North Korean leader can give orders and receive news and briefings.

Trips shrouded in secrecy

For Kim Jong-un's predecessors, trips were often secret until after they ended.

Experts still couch their estimates of how many times North Korean leaders have travelled abroad because some trips may still remain secret.

The Chinese and North Korean media are not much help. They are state run and follow the directives of their respective ruling parties.

Kim Jong-il's trip to China in 2003, for example, was not announced until days later.

When he took the train across Russia to visit President Dmitry Medvedev in 2009, local photographers were reportedly banned from documenting the journey through their country.

Whole towns in Siberia were instructed to stay indoors and keep off the streets until the train safely passed. Kim Jong-un's journey this week showed how much times have changed.